California fire risk to worsen this weekend, last through Thanksgiving

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BUTTE COUNTY, CA – NOVEMBER 09: A lone burro is tied to a Highway 70 sign post with a bucket of water in the evacuated Camp Fire burn area south of Chico, Calif., November 9, 2018. (Karl Mondon/Bay Area News Group)

PARADISE, CALIFORNIA – NOVEMBER 9: A charred vehicle was left in the middle of Honey Run Road in Paradise, Calif., on Friday, Nov. 9, 2018. (Ray Chavez/Bay Area News Group)

PARADISE, CALIFORNIA – NOVEMBER 9: Clothes hang in a property on Edgewood Lane in Paradise, Calif., on Friday, Nov. 9, 2018. Authorities said they found bodies in the Edgewood area. (Ray Chavez/Bay Area News Group)

PARADISE, CALIFORNIA – NOVEMBER 9: A hen walks around to find something to eat in a property on Honey Run Road in Paradise, Calif., on Friday, Nov. 9, 2018. (Ray Chavez/Bay Area News Group)

DUBLIN, CA – NOVEMBER 9: The sun rises through smoke in Dublin, Calif. on Friday, November 9, 2018. The fire from the Camp Fire in Paradise has swept through the Bay Area. (Sarah Dussault/Bay Area News Group)

DUBLIN, CA – NOVEMBER 9: The sun rises through smoke in Dublin, Calif. on Friday, November 9, 2018. The fire from the Camp Fire in Paradise has swept through the Bay Area. (Sarah Dussault/Bay Area News Group)

PARADISE, CA – NOVEMBER 08: Firefighters begin a back burn against the Camp Fire on Pentz Road south Paradise, Calif., Thursday, November 8, 2018. (Karl Mondon/Bay Area News Group)

CHICO, CALIFORNIA – NOVEMBER 8: Camp Fire evacuees covered with blankets provided. by the Red Cross at a evacuee center at the Neighborhood Church in Chico, Calif., on Thursday, Nov. 8, 2018.(Ray Chavez/Bay Area News Group)

California’s fire risk, already at very dangerous levels with massive fires burning in Butte County, Malibu and other locations, is only going to worsen this weekend, and is likely to continue at least through Thanksgiving.

On Friday afternoon, the National Weather Service issued a red flag warning for the Bay Area beginning Saturday night at 10 p.m. and continuing through Sunday at 4 p.m.

Citing “critical fire weather conditions,” the agency said that wind gusts blowing from dry inland areas toward the ocean could reach up to 60 mph in the East Bay hills, Santa Cruz Mountains and North Bay hills, with high temperatures in the 70s and humidity in the bone-dry single digits.

“There’s no relief in sight for now,” said Carolina Walbrun, a forecaster with the National Weather Service in Monterey. “The danger remains. The underlying conditions remain.”

A similar red flag warning remained through Friday night in Los Angeles and Ventura counties, with the National Weather Service saying dire conditions are expected again there from Sunday through Tuesday. Santa Ana winds of up to 70 mph and low humidity will bring “a near imminent chance of widespread critical fire weather conditions,” and rapid spread of any fires that are started, forecasters said in an urgent bulletin.

Perhaps more ominous, there is no rain forecast for Northern or Southern California for at least the next 10 days.

That means that every warm, dry windy day between now and then will only further dry out shrubs, trees and grasses. A single spark could well cause more fires like the ones that leveled the town of Paradise in Butte County Thursday night, killing at least nine people, and which raged over hillsides in Ventura and Los Angeles counties in Southern California on Friday, burning celebrity homes and causing more than 150,000 people to evacuate in the three areas, according to Cal Fire officials.

Experts offered stark advice.

“Be careful. Pray for rain,” said Craig Clements, director of the Fire Weather Research Laboratory at San Jose State University.

Clements on Friday afternoon was driving back from Butte County, where he and his students were sampling fire behavior. He said he was shocked at how quickly the Camp Fire spread, rushing across roughly 90,000 acres — an area more than twice the size of San Francisco — in about 18 hours. The fire consumed 80 acres a minute, blackening an area the size of a football field every second as residents fled for their lives in chaotic traffic jams.

“The fire was moving very fast. It was very windy and turbulent,” he said. “Winds 200 feet above the ground were blowing at 40 mph. It spread very very fast.”

These abandoned and burned out cars shows you what a panic it must have been for residents trying to escape the Camp Fire. Unreal scenes in Paradise, CA, this morning. #CampFirepic.twitter.com/AhBuWzS0Tx

Clements noted that October is usually the most dangerous month of the year in California for wildfires. Because it has often been roughly six months since the state experienced any significant rain, vegetation is the driest and most flammable that it gets all year. Many of the state’s most devastating fires, from the 1991 Oakland Hills blaze to last year’s deadly Wine Country fires, happened in October.

Usually by Thanksgiving, however, some rain has fallen, dampening the ground and easing the risk that fallen power lines, campfires, or sparks from outdoor equipment and vehicles will set off an inferno. But not this year.

“The fuels are critically dry and they are only getting worse,” Clements said. “And now we are getting strong winds. This is a crazy year.”

The dry, warm weather in recent months has been caused by a persistent ridge of high pressure over the Pacific Ocean.

Increasingly, as the Earth’s climate continues to warm, such ridges have been lasting longer into the fall months, said Daniel Swain, a UCLA climate scientist. California’s temperatures in the fall are about 3 degrees Fahrenheit warmer now than they were in 1980, and rainfall has dropped by about one-third in the autumn, he noted.

That means fire season is lasting longer. And big blazes into Thanksgiving or later will increasingly be the normal in California for generations to come, he said.

“We are seeing a pattern. It’s happening in Southern California, but it’s also starting to happen in Northern California,” Swain said.

Since July 1, San Francisco has only received .21 inches of rain — or roughly enough to fill a bottle cap. If November ends with no more ran than that, it would be the third-driest such period back to 1849, during the Gold Rush, when San Francisco’s weather records began.

That doesn’t bode well for the upcoming winter rain season. Only 26 other times since 1849 has San Francisco seen such little rain from July 1 to Oct. 31. In only eight of those times has the city ended the winter with an average or above-average rainfall year, according to data from Jan Null, a meteorologist with Golden Gate Weather Services in Saratoga.

The slow start to the rainy season this year is not a guarantee of a new drought, however. Three years ago, in the 2015-2016, San Francisco had received the same amount of rain, .20 inches, by Oct. 31, but ended up with 98 percent of normal. And during its wettest year ever, 1862-63, storms caused massive flooding and ended the year with 208 percent of normal rain, even though the winter had begun with only .02 inches by Oct. 31.

Still, Null notes, radar and computer modeling shows no storms on the horizon for at least the next 10 days, with the first possibility of a weather system arriving from the Pacific the day before Thanksgiving.

“Because it’s so far out, it’s not the sort of thing I would be placing money on,” Null said. “But it bears watching.”

Paul Rogers has covered a wide range of issues for The Mercury News since 1989, including water, oceans, energy, logging, parks, endangered species, toxics and climate change. He also works as managing editor of the Science team at KQED, the PBS and NPR station in San Francisco, and has taught science writing at UC Berkeley and UC Santa Cruz.

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